Process to produce carbon nanotubes from carbon rich wastes

ABSTRACT

We disclose a process to produce carbon nanotubes from microalgae. Microalgae is been utilized for biodiesel production. The algal membrane resulted from oil extraction of microalgae is used here to produce carbon nanotubes. The process utilized for the conversion is composed of two steps, in the first step the algal membrane is converted to carbon black through a pyrolysis process in inert atmosphere, in the second step the resulted carbon black is converted to carbon nanotubes by mixing the carbon black with a fluid with known self ignition condition and subjecting the mix to said self ignition condition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/647,439, filed Dec. 26, 2009, the entirety ofwhich is incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to a process to produce carbon nanotubes frommicroalgae.

BACKGROUND OF THE INVENTION

Photosynthetic organisms such as microalgae are being utilized toproduce biodiesel by converting organic molecules to lipids that canthen be converted to biodiesel. These photosynthetic organisms are farfrom monolithic. Biologists have categorized microalgae in a variety ofclasses, mainly distinguished by their pigmentation, life cycle andbasic cellular structure. The four most important (at least in terms ofabundance) are: The diatoms (Bacillariophyceae), green algae(Chlorophyceae), blue-green algae (Cyanophyceae) and the golden algae(Chrysophyceae).

Microalgae are a primitive form of plants. Microalgae grow in aquaticenvironments. Microalgae, like higher plants, produce storage lipids inthe form of triacyglycerols (TAGs). Although TAGs could be used toproduce of a wide variety of chemicals, in here we will focus on theproduction of fatty acid methyl esters (FAMEs), which can be used as asubstitute for fossil-derived diesel fuel. This fuel, known asbiodiesel, can be synthesized from TAGs via a simple transesterificationreaction in the presence of acid or base and methanol. Biodiesel can beused in unmodified diesel engines, and has advantages over conventionaldiesel fuel in that it is renewable, biodegradable, and produces lessSO_(x) and particulate emissions when burned.

The algal membrane resulted from the extraction of lipids has beenproposed for different uses such as animal feed or plant nutrients. Whenunconventional algal feed such as sewage are used for the microalgaegrowth, the membrane cannot be easily utilized as animal feed withoutfurther treatment.

This invention is disclosing a process to convert the algae membrane tocarbon nanotubes. Conventional methods for production of carbonnanotubes include chemical vapor deposition, laser ablation and arcdischarge methods. All of these methods require pure carbon source forthe production of carbon nanotubes (see Graham et al. U.S. Pat. No.7,635,867 and Liu et al. U.S. Pat. No. 7,625,544)

This invention utilizes the algae membrane as a source for nanotubesproduction.

SUMMARY OF THE INVENTION

This invention relates to process for production of carbon nanotubesusing algae as source material. The algae membrane is converted tocarbon black using a pyrolysis process. The carbon black is then mixedwith a substance, preferably in liquid form, with known self-ignitionconditions. The carbon black is then is placed in a sealed chamber. Thechamber is then promoted to the self-ignition condition. Upon theignition of the substance in the chamber, without external flam, theenergy released from the ignition produces carbon nanotubes out of thecarbon black. The process is repeated to increase the purity of theproduced carbon nanotubes.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 Microscopic image showing algal membrane following oil extraction

FIG. 2 Thermogravitmetric analyses showing the formation of carbon blackwhen pyrolysis process is performed on the algal membrane. Algae wasobtained following different feeding schemes; sewage, cellulose, etc.

FIG. 3 SEM monograph showing carbon black particulates

FIG. 4 SEM monograph showing the formation of carbon nanotubes.

FIG. 5 Thermogravitmetric analyses showing the purity of carbonnanotubes. The carbon nanotubes are estimated at 72%.

FIG. 6 SEM monograph of purified carbon nanotubes

FIG. 7 TEM monograph showing the purified carbon nanotubes.

DESCRIPTION OF THE INVENTION

Before disclosing embodiments of the invention, it is to be understoodthat the invention is not limited to the details of construction orprocess steps set forth in the following description. The invention iscapable of other embodiments and of being practiced or being carried outin various ways.

As used in this specification and the appended claims, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly indicates otherwise. Thus, for example, reference to “a chamber”includes a mixture of two or more chambers, and the like.

As used in this specification and the appended claims, microalgae andalgae describes the microorganism used in this invention to convert itscontent to carbon nanotubes.

The invention describes a process that converts waste of biodieselproduction into carbon nanotubes. The aspects of the invention pertain aprocess that yields the maximum amount of carbon nanotubes generatedfrom carbonated waste material.

In a preferred embodiment of this invention the source material areintact algae before oil extraction. In another preferred embodiment thesource material is algal membrane obtained after oil extraction. In yetanother preferred embedment of this invention the source material is acarbon rich waste product such as rubber, plastics, wood, biomass, drysewage, jojoba shells, etc.

The source material such as algae is processed in heating chamber underinert atmosphere to produce carbon black; the heating scheme utilized inthe pyrolysis process is at high rate, such as 10-50° C./min. In anotherembodiment the heating rate can be slow at 1-10° C./min. The heatingchamber used in the heating process is a closed container that cansustain the heating process. In another embodiment the heating source isfrom a solar source. The chamber is maintained at inert condition duringthe heating process.

The carbon black is mixed with a substance that has manageableauto-ignition conditions. Though the mixing ratio between theauto-ignition substance and the carbon black is function of the amountof energy release generated from the auto-ignition substance, apreferred mixing ratio is 100-200 ml for auto ignition substance to 1 kgof carbon black.

Auto-ignition substances operate under different pressure andtemperature conditions. Though these conditions are known to experts inthe field, a tabulated list is presented to show the auto-ignitionconditions for some of the compounds.

Auto ignition temperature ° C. at Compound 1 bar 2 bar 5 bar 10 barn-Hexane 230 235 210 197 n-Heptane 220 201 197 190 n-Octane 215 210Benzene 565 526 470 451 Methanol 440 283 250 Ethanol 400 283 250 Acetone525 350 275 260 Dioxan 375 212 197 189

The prepared carbon black is then placed in a sealed chamber. Thechamber is prompted to the auto-ignition condition of the mixedsubstance. Once the chamber reaches the auto-ignition condition a noisemarking the auto-ignition condition will be generated. The chamber isthen allowed to cool down to room temperature. The sample is then takento quantify the formation of carbon nanotubes. The process of bringingthe chamber to auto-ignition condition can be repeated, depending on thepurity of the generated carbon nanotubes, i.e two repeated operationsincreases the purity of the generated carbon nanotubes. The purityformed carbon nanotubes out of a single operation is between 70-80% andfor double operations between 75-85%.

In order to enhance the purity of formed carbon nanotubes, purificationby wet or dry techniques can be utilized. In the wet techniquesoxidizing agents as those described in the literature such as H₂O₂, canbe utilized to increase the sample purity. Following this technique thepurity reached 90%. Another technique that is disclosed in thisinvention is the use of ionic liquid to increase the purity of theformed carbon nanotubes. In dry technique slow burning process isutilized to increase the purity of the formed carbon nanotubes.

EXAMPLE

In one preferred mix, carbon black generated from burning microalgaemembrane (FIG. 1) in inert conditions. FIG. 2 shows the carbon blackgenerated when burning microalgae membrane in nitrogen environment. FIG.3 shows a scanning electron microscopy monograph of the generated carbonblack. A kilogram of carbon black is mixed with 200 milliliter ofethanol then placed in a sealed chamber. The chamber pressure andtemperature were raised to 10 bars and 250° C. using an external propaneburner. When the ethanol auto-ignited a noise is generated in thechamber and sudden drop in the pressure is observed. The chamber wasthen allowed to cool to room temperature using natural cooling. Thesample was then taken out of the chamber for analysis. FIG. 4 showsscanning electron micrograph of the formed carbon nanotubes. The purityof the formed carbon nanotubes is evaluated using thermogravitmetricanalysis as shown in FIG. 5. The purity was estimated to be 75%. Ionicliquid made by mixing two fatty acids (capric acid (C₁₀H₂₀O₂) and lauricacid (C₁₂H₂₄O₂)) was utilized to purify the carbon nanotubes. FIG. 6shows scanning electron microscope monographs of purified carbonnanotubes. FIG. 7 shows transmission electron microscope of purifiedcarbon nanotubes.

1. A method of forming carbon nanotubes from carbon rich waste,comprising: heating the carbon rich waste in an inert atmosphere to formcarbon black; mixing the carbon black with at least one auto-ignitionsubstance; and converting the carbon black to carbon nanotubes in asealed chamber by heating a mixture of the carbon black and theauto-ignition substance.
 2. The method of claim 1, wherein heating thecarbon rich waste comprises heating the carbon rich waste selected fromthe group consisting of rubber, plastics, wood, jojoba shells and drysewage.
 3. The method of claim 1, wherein converting the carbon black tocarbon nanotubes comprises converting the carbon black to carbonnanotubes that include at least one multiwall carbon nanotube.
 4. Themethod of claim 1, further comprising purifying the carbon nanotubes viaa dry purification method.
 5. The method of claim 4, wherein purifyingthe carbon nanotubes via a dry purification method comprises heating theunpurified nanotubes to above 500 degrees Celsius.
 6. The method ofclaim 1, further comprising purifying the carbon nanotubes via a wetpurification method.
 7. The method of claim 6, wherein purifying thecarbon nanotubes via a wet purification method comprises purifying thecarbon nanotubes with an ionic liquid.
 8. The method of claim 7, whereinpurifying the carbon nanotubes via a wet purification method comprisespurifying the carbon nanotubes with an ionic liquid that is a mix offatty acids.
 9. The method of claim 7, wherein purifying the carbonnanotubes via a wet purification method comprises purifying the carbonnanotubes with an ionic liquid at room temperature.
 10. The method ofclaim 7, wherein purifying the carbon nanotubes via a wet purificationmethod comprises purifying the carbon nanotubes with at least oneoxidizing agent.
 11. The method of claim 7, wherein purifying the carbonnanotubes via a wet purification method comprises purifying the carbonnanotubes with at least one acid.
 12. A method of forming carbonnanotubes from carbon rich waste, comprising: heating the carbon richwaste in an inert atmosphere to form carbon black; mixing the carbonblack with at least one auto-ignition substance; converting the carbonblack to carbon nanotubes in a sealed chamber by heating a mixture ofthe carbon blade and the auto-ignition substance; and purifying thecarbon nanotubes via a dry purification method.
 13. The method of claim12, wherein heating the carbon rich waste comprises heating carbon richwaste selected from the group consisting of rubber, plastics, wood,jojoba shells and dry sewage.
 14. The method of claim 12, whereinconverting the carbon black to carbon nanotubes comprises converting thecarbon black to carbon nanotubes that include at least one multiwallcarbon nanotube.
 15. The method of claim 12, wherein purifying thecarbon nanotubes via a dry purification method comprises heating theunpurified nanotubes to above 500 degrees Celsius.
 16. A method offorming carbon nanotubes from carbon rich waste, comprising: heating thecarbon rich waste in an inert atmosphere to form carbon black; mixingthe carbon black with at least one auto-ignition substance; convertingthe carbon black to carbon nanotubes in a sealed chamber by heating amixture of the carbon blade and the auto-ignition substance; andpurifying the carbon nanotubes via a wet purification method.
 17. Themethod of claim 16, wherein converting the carbon black to carbonnanotubes comprises converting the carbon black to carbon nanotubes thatinclude at least one multiwall carbon nanotube.
 18. The method of claim16, wherein purifying the carbon nanotubes via a wet purification methodcomprises purifying the carbon nanotubes with an ionic liquid.
 19. Themethod of claim 18, wherein purifying the carbon nanotubes via a wetpurification method comprises purifying the carbon nanotubes with anionic liquid that is a mix of fatty acids.
 20. The method of claim 18,wherein purifying the carbon nanotubes via a wet purification methodcomprises purifying the carbon nanotubes with an ionic liquid at roomtemperature.
 21. The method of claim 18, wherein purifying the carbonnanotubes via a wet purification method comprises purifying the carbonnanotubes with at least one oxidizing agent.
 22. The method of claim 18,wherein purifying the carbon nanotubes via a wet purification methodcomprises purifying the carbon nanotubes with at least one acid.